U.S. patent number 4,643,563 [Application Number 06/634,056] was granted by the patent office on 1987-02-17 for color image data processing method.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Kazuo Sayanagi.
United States Patent |
4,643,563 |
Sayanagi |
February 17, 1987 |
Color image data processing method
Abstract
There is provided a color image data processing method for
reproducing a color image by use of micro color points of a
plurality of colors. The processings for every region to obtain the
areas of the color points are performed in parallel irrespective of
which region in a plurality of regions on the chromaticity chart
the color which should be reproduced belongs to, and among the
respective processing results, the color points whose areas were
determined to be positive values are used, thereby reproducing a
color image.
Inventors: |
Sayanagi; Kazuo (Yokohama,
JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
|
Family
ID: |
15258456 |
Appl.
No.: |
06/634,056 |
Filed: |
July 25, 1984 |
Foreign Application Priority Data
|
|
|
|
|
Jul 29, 1983 [JP] |
|
|
58-139994 |
|
Current U.S.
Class: |
355/77; 356/405;
356/406; 358/518 |
Current CPC
Class: |
H04N
1/60 (20130101) |
Current International
Class: |
H04N
1/60 (20060101); G01N 021/25 () |
Field of
Search: |
;355/32,35,77
;356/405,406,407,410,402,425 ;364/525,526 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hix; L. T.
Assistant Examiner: Rutledge; D.
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Claims
What is claimed is:
1. A color image data processing method comprising the steps
of:
receiving, as input data, a plurality of color component values
representing a color picture element to be reproduced;
performing in parallel a plurality of operations for a respective
plurality of predetermined regions in a color coordinate system on
the chromaticity chart of the color of the picture element, wherein
areas for a predetermined number of colors to reproduce the picture
element are determined by applying the operations to the plurality
of color component values; and
selecting a result of an operation that provides positive values
for the areas for using those areas to reproduce the picture
element.
2. A method according to claim 1, wherein the color component
values are three stimulus specifications and the areas used to
reproduce the picture element are obtained from three stimulus
specifications of the color to be reproduced.
3. A method according to claim 2, wherein the picture element is
reproduced by using cyan, magenta and yellow.
4. A method according to claim 1, further comprising the steps
of:
discriminating positive and negative values of the areas obtained
in said performing step; and
selecting the values determined to be positive in said
discriminating step.
5. A method according to claim 1, wherein a color reproduction
range to be reproduced is divided into six regions on the
chromaticity chart.
6. A method according to claim 5, wherein said six regions are
divided by the respective cyan, magenta, yellow, red, blue, green,
and white points on the chromaticity chart.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color image data processing
method for reproducing a color image by use of micro color points
of a plurality of colors.
2. Description of the Prior Art
In conventional printing, micro color points of each color of,
e.g., cyan C, magenta M, yellow Y, and black K are used and by
making the areas of color points different, various colors are
reproduced.
The area of the color point of each color has been conventionally
determined by performing processings such as masking processing,
undercolor removal and inking in consideration of unnecessary
absorption of respective colors of Y, M, C, and K which are
actually used for the density at which the printing should be done
on the basis of photograph technology. However, it is
conventionally well known that this method is imperfect since the
densities which are used have various problems. It is an old method
in printing that the chrominance calculations are carried out with
respect to eight colors of Y, M, C, K, red R, green G, blue B, and
white W. An example of these chrominance calculations is disclosed
in H. E. Neugebauer, "Z. Photo. 34 (4)", pages 73-89, 1937; A. C.
Hardy et al, "J. Opt. S Am 38", pages 300-307, 1948, and the
like.
However, in these examples, it is difficult to obtain the area of
the color point as an unconditional solution due to the
calculations since a number of (eight) colors are handled.
Therefore, the following method has been proposed. Namely, in case
of printing, since the rentinal points of different colors overlap,
the color points of eight colors finely appear and it is therefore
impossible to obtain the unconditional solution to derive three
retinal point areas which can realize the color which should be
reproduced. On the other hand, if the number of colors which are
used for reproduction is limited to (R, G, B), (Y, M, C), K, and W,
the calculations can be easily solved. A parenthesis ( ) denotes
that one of the colors which are included therein is selected.
However, different coefficients have to be used for six kinds of
different combinations of primary colors used, namely, for six
regions for color reproduction.
These six regions are represented by chromaticity coordinates of
color reproduced; they are as shown in FIG. 1. In the chart,
coordinates x and y are so-called variables indicating the
chromaticity, and total seven points consisting of standard
chromaticity Y, M and C of DIN, and R, G, B, and white point which
are caused by them are represented as PY, PM, PC, PR, PG, PB, and
PW, respectively.
The calculating expression to obtain the color point area in each
region is the similar linear expression with three unknowns as that
of the masking processing in the photograph and is of the same type
of equation as a form. A different point is that the color
densities of three layers are used as the variables in the
photograph, while color stimulus specifications of three colors
(simply, chrominance signals of three colors at the light
intensity) are used in this case. Also in this case, different
calculations have to be performed in six regions.
On the other hand, in case of executing a plurality of different
calculation processings in accordance with the color which should
be reproduced, two methods are considered:
(i) the chromaticity is examined and it is discriminated to see
which region the chromaticity belongs to, then the correct
processing is selected and the calculation is performed;
(ii) look-up tables for the inputs and outputs are prepared in the
whole chromaticity range and they are referred to. However, the
method (i) needs the additional calculation for discrimination, so
that this delays processing. The method (ii) requires a large
storage device and in the case where the chromaticity of color
point or three stimulus specifications which are used for color
reproduction, namely, when the condition for color reproduction is
changed, the content of the storage device has to be all
replaced.
SUMMARY OF THE INVENTION
The present invention is made in consideration of the
above-mentioned problems and intends to provide a color reproducing
method which can remarkably shorten the calculation processing time
without requiring a large-scale storage device.
Also, another object of the invention is to provide a color
reproducing method which can cope with the change of condition for
color reproduction by merely changing only a few constants.
The above and other objects and features of the present invention
will be apparent from the following detailed description in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing six regions in the IOC color
coordinates; and
FIG. 2 is a diagram showing a circuit to perform the color
reproduction processing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
One embodiment of the present invention will now be described
hereinbelow. First, the calculating expression in each region will
be obtained. Three stimulus specifications of each primary color
are represented as shown in the following table.
______________________________________ Primary Three stimulus
Relation in colors specifications magnitude
______________________________________ W X.sub.w, Y.sub.w, Z.sub.w
Can be all normalized to 1. Y X.sub.y, Y.sub.y, Z.sub.y X.sub.y,
Y.sub.y > Z.sub.y M X.sub.m, Y.sub.m, Z.sub.m X.sub.m, Z.sub.m
> Y.sub.m C X.sub.c, Y.sub.c, Z.sub.c Y.sub.c, Z.sub.c >
X.sub.c R X.sub.r, Y.sub.r, Z.sub.r X.sub.r > Y.sub.r, Z.sub.r G
X.sub.g, Y.sub.g, Z.sub.g Y.sub.g > X.sub.g, Z.sub.g B X.sub.b,
Y.sub.b, Z.sub.b Z.sub.b > X.sub.b, Y.sub.b K X.sub.k, Y.sub.k,
Z.sub.k All are about 0. ______________________________________
It is assumed that the three stimulus specifications of the
reproduction color (for instance, point A in the chromaticity chart
in FIG. 1) which should be reproduced by a color printer are X, Y
and Z; that the respective point areas of the respective colors R,
G, B, Y, M, C, K, and W are a.sub.r, a.sub.g, a.sub.b, a.sub.y,
a.sub.m, a.sub.c, a.sub.k, and a.sub.w ; and that the reproduction
color lies in a region I of FIG. 1. At this time, it is possible to
represent as follows. ##EQU1##
Solutions of a.sub.w, a.sub.y, a.sub.r, and a.sub.k can be obtained
from this expression (1).
On the other hand, by substituting the first simple expression in
expression (1) for the second to fourth expressions therein,
following expression (2) will be derived. ##EQU2## The above
expression (2) can be also conversely easily solved similarly to
expression (1).
Since these expressions (1) and (2) are so-called linear equations
with four unknowns or linear equations with three unknowns, they
can be solved by use of a matrix.
For example, now assuming that the respective three color stimulus
specifications in the example of FIG. 1 are ##EQU3## expression (3)
will be obtained as the solutions of expression (2) in the region
I, ##EQU4## and expression (4) will be further derived in a region
II, ##EQU5## Expressions can be also similarly obtained with
respect to the other four regions.
In these expressions, a.sub.y, a.sub.r and a.sub.k indicate the
areas in which the primary colors Y, R and K appear,
respectively.
On the other hand, in case of realizing a.sub.y, a.sub.r and
a.sub.k due to the print by means of the overlapping of the areas
of color points (retinal points) of Y, M and C which has been
conventionally considered, they are obtained by coaxially
overlapping the respective points of Y, M and C. For example, in
the case where the color points are sequentially overlapped on a
recording paper in accordance with the order of Y, M and C, the
areas a.sub.Y, a.sub.M and a.sub.C which are actually formed with
respect to Y, M and C satisfy the relation of a.sub.Y >a.sub.M
>a.sub.C and can be represented by expression (5). ##EQU6## In
the digital print whereby the color points are coaxially dotted, by
conversely solving the above expression (5), the expression can be
represented by expression (6). ##EQU7## Expression (3) and the like
can be converted to a.sub.Y, a.sub.M and a.sub.C by use of the
relation of expression (6). For instance, in correspondence to
expression (3), we will have ##EQU8## Similarly, the areas a.sub.Y
in the other regions are expressed as follows. ##EQU9## The
respective coefficients of the respective expressions with regard
to these six regions extremely differ. The areas a.sub.M and
a.sub.C can be also expressed for every region and their
coefficients also differ.
FIG. 2 is a diagram showing a circuit to perform the processings as
mentioned above. In the diagram, numerals 2-1 to 2-6 denote matrix
circuits and the circuit 2-1, for example, performs the matrix
arithmetic operation shown in expression (7). Numerals 4-1 to 4-6
indicate positive-negative decision circuits to discriminate
between positive and negative in the outputs of the matrix circuits
2-1 to 2-6, respectively; 6-1 to 6-6 are latch circuits; 8, 9 and
10 are input signal lines for the color stimulus values X, Y and Z
of the color which should be reproduced; 12 shows an address line
and data line from a host computer (not shown); 14 and 16 are
timing signal lines from the host computer; and 18 shows
positive-negative discriminating signal lines which are output from
the positive-negative decision circuit 4-1 to 4-6.
The color stimulus specifications X, Y and Z of the color which
should be reproduced are input as the digital signals in parallel
to the matrix circuits 2-1 to 2-6 in response to a timing pulse
TP1. The matrix circuit 2-1 carries out the matrix arithmetic
operation shown in expression (7), while the other matrix circuits
2-2 to 2-6 execute the matrix arithmetic operations in accordance
with the respective regions II to VI. Now assuming that the
location on the chromaticity chart of the color to be reproduced is
point A in FIG. 1, the output data a.sub.Y, a.sub.M and a.sub.C of
the matrix circuit 2-1 are all positive values. However, either one
or two of the respective output data a.sub.Y, a.sub.M and a.sub.C
of the other matrix circuits 2-2 to 2-5 become certainly negative
values. Thus, only the positive-negative discriminating signal line
18 of the positive-negative decision circuit 4-1 becomes a high
level and the other signal lines 18 become a low level. Therefore,
the output data a.sub.Y, a.sub.M and a.sub.C of only the latch
circuit 6-1 are latched and the data are read out in response to a
timing pulse TP2. No data is latched in the other latch circuits
6-2 to 6-6.
As described above, since only the matrix circuit of which all
output data have positive values among the matrix circuits 2-1 to
2-6 is selected, the correct solution in accordance with the region
on the chromaticity chart is obtained without performing the
processing for discrimination of region before the matrix
arithmetic operation. In addition, the matrix circuits 2-1 to 2-6
can be changed through the address and data line 12 from the host
computer.
Although the case where the region was divided into six subregions
has been described above, in the case where the color points of R,
G and B each having particularly high purity are used for color
reproduction, it is enough that only Y among Y, M and C may be
added or Y and M may be added. In such a case, the region is
divided into four or five subregions and also the number of matrix
circuits may be four or five. In addition, the invention can be
also accomplished by disenabling a portion of matrix circuits by
the host computer.
As described above, according to the present invention, there is no
need to examine to which region the color which should be
reproduced belongs before calculation processing, thereby enabling
the processing time to be remarkably reduced. In addition, a
storage device with large capacity is unnecessary. Further, it is
possible to quickly cope with changes in the color reproduction
condition.
* * * * *